During the last decades the sizes of wafer features has dramatically decreases. The dimensions of these feature is well below one micron and is expected to shrink during the next coupled of years. Accordingly, the importance of resolution enhancing microscopy solutions has dramatically increased.
The resolution of a microscope is dependent upon various parameters including the numerical aperture (NA) of the microscope and especially the numerical aperture of the objective lens of the microscope. The numerical aperture can be increase by increasing the refractive index of a medium between the wafer and the lens.
A brief description of immersion microscopy is provided in the following documents: “DUV Water Immersion Technology Extends Linearity First Results From the new 65 nm Node CD Metrology System LWM500 WI”, F. Hillmann, H. J. Bruck, A. Bosser, www-vistec-semi.com; PCT patent application publication serial number WO 2006/113916 titled “Crytogenic immersion microscope” and U.S. Pat. No. 5,900,354 of Batchelder titled “Method for optical inspection and lithography”.
One method of immersion microscopy includes placing a drop of fluid between an objective lens of an inspection system and between an inspected wafer. The inspection process includes scanning the wafer by introducing a relative movement between the wafer and the objective lens.
The upper surface of the wafer includes three dimensional features. When these features are being scanned the drop of fluid can be deformed and, additionally or alternatively, can loose fluid in an unexpected manner. In addition, the scanning speed can be limited in order to limit drop deformations.
It is further noted that this scanning can spread contaminations over the inspected wafer, some contaminations can be initially located at the wafer edges while other contaminations can result from the objective lens or other components of the inspection system.
The mentioned above fluid should comply with various contradicting results: (i) the fluid should not damage the wafer, (ii) the fluid should have a high enough refractive index, (iii) the fluid should be relatively transparent, and (iv) the fluid should be relatively viscose such as to be able to propagate over various features without breaking apart.
There is a need to provide an efficient method and system for Auger spectrometry.